EGR coolers have been utilized for a number of years in both combustion and spark ignition engines. The early patent to Cook, U.S. Pat. No. 3,937,196 shows an internally mounted EGR cooler. EGR coolers are currently being used on engines such as the 6.0 L POWER STROKE® and 4.5 L diesel engines as OEM components.
The EGR cooler is a component in the exhaust gas recirculation circuit or system that is typically coupled to an internal combustion engine in an effort to reduce the engine's noxious emissions. The EGR cooler collects a portion of the engine exhaust, and routs it back for re-injection into the engine intake manifold. Prior to reinjection the exhaust gas is typically cooled. Cooling re-injected exhaust tends to reduce the combustion temperature of the engine which tends to have the desired effect of reducing nitrogen oxide (“NOX”) emissions. However, the reduction in NOX, typically comes at the cost of reduced engine efficiency.
The EGR cooler is a heat exchange unit that utilizes engine coolant to remove heat from the exhaust gas flowing through it. The heat exchanger design keeps the coolant and exhaust gas from mixing, but allows for heat to flow from the exhaust gas to the engine coolant. This can be achieved with a shell structure, with tubes being routed through the shell-which typically also includes a structure to facilitate heat transfer. Engine coolant is input to the EGR cooler where through the design of the heat exchange elements, heat is transferred to the coolant. The coolant and removed heat exit the EGR cooler where the coolant eventually ends up in the water jacket of the engine where it is cooled by the engine cooling system.
In summary, the EGR cooler is a heat exchange unit through which engine coolant can circulate to extract heat from a portion of the spent exhaust gases which are cooled and re-directed back to the engine intake manifold such that their re-combustion tends to reduce the creation of NOX (nitrogen oxide) vehicle emissions.
Conventional or stock EGR coolers can often fail for various reasons. Their failure may be catastrophic, or a degradation of performance. Lack of coolant flow can lead to one particular catastrophic failure mechanism, which causes excessive heat build up, and subsequent failure in the EGR cooler. The EGR cooler is designed for a particular operating temperature by the manufacturer, and if heat builds up causing the temperature to rise beyond specification the unit can fail, with disastrous results for the entire engine. Coolant supply to the EGR cooler may be reduced due to a decreased flow rate, or by blockages reducing the amount of coolant circulating.
A particular problem arises in diesel engines having an oil cooler through which coolant flows, where the oil cooler is disposed in front of the coolant input to the EGR cooler. In such a system it is typically not uncommon for coolant flow through the oil cooler to become restricted, subsequently reducing the coolant available to the EGR cooler. If coolant flow to the EGR cooler is reduced, the EGR cooler can be subjected to excessively high exhaust gas temperatures.
The resulting extreme temperature rise in the EGR cooling unit can rupture or crack the internal pathways of the EGR cooler. Ruptures can occur due to reduced coolant flow causing temperatures above the boiling point of the coolant. The coolant may “flash boil” in the EGR cooler, especially if circulation is reduced allowing the coolant to remain on the hot spot long enough to boil. Boiling can cause a rupture within the EGR cooler when the liquid coolant is suddenly turned into an expanding gas. This rupturing can lead to the mixing of the exhaust and engine coolant through the in ruptures or cracks in the EGR cooler. This type of catastrophic malfunction can cascade into the other engine systems, damaging the engine and its associated components.
Another failure causing reduced effectiveness of the EGR cooler, and degraded EGR system performance can arise due to the internal configuration of the conventional EGR cooler. In conventional OEM EGR cooler designs only a few tubes (typically oval in shape) are incorporated in the construction. The tubes may contain baffling, or thin heat exchange fins on the interior of the tube as a heat exchanging structure. Exhaust gas flows through the interiors of the tubes, and coolant flows over the exterior of the tubes and is contained in the EGR housing. The engine coolant circulates through the EGR cooler shell or housing around the exterior of the tubes and the exhaust gases flow through the interior of the tubes over the fins, cooling the exhaust gas. This finned structure can lead to another failure mechanism through clogging of the exhaust gas passage ways.
The conventional tube and fin heat exchange EGR cooler designs can become clogged over time due to a build up of particulates that can be found in the exhaust and other factors, resulting in substantially reduced heat transfer capability and higher exhaust gas temperatures in the intake manifold. The higher temperature re-circulated exhaust gas leads to increased NOX production due to higher combustion temperatures.
Accordingly, there exists a need for an improved EGR cooler that is less prone to catastrophic failure and performance degradation, including clogging in the exhaust passage ways, rupturing when coolant flow is reduced, and other failure, or performance reducing mechanisms. For efficiency's sake it is further desirable to provide a method of rebuilding salvaged conventional EGR coolers to solve the abovementioned, and other problems.